Highly absorbent hydrogel materials, typically slightly cross-linked hydrophilic polymers, are known and have been suggested for use in absorbent structures. These materials have a high absorbent capacity for deionized water, typically on the order of 100 times their own weight or more. The absorbent capacity of these materials for body fluids like urine or menses is dramatically lower than for deionized water. It is generally believed that the dramatically lower absorbent capacity for such fluids is caused by the electrolyte content of these fluids and the phenonenon is therefore referred to as the "salt poisoning" effect. It is desirable to increase the absorbent capacity of hydrogels for body fluids so that these materials can be put to a more economical and efficient use.
It is therefore an object of this invention to provide absorbent structures comprising a hydrogel having an increased absorbent capacity for electrolyte-containing fluids. It is a further object of this invention to provide disposable absorbent products, like disposable diapers and sanitary napkins, comprising the absorbent structures of the present invention.
U.S. Pat. No. 4,026,291, issued May 31, 1977 to Nagano et al., discloses the use of diethyl amino cellulose in the absorbent core of an article for treating secreted human fluids. The purpose of the ion exchange fibers in the core is to deodorize, sterilize and coagulate the secreted fluids.
Japanese Patent Application OPI No. 118,846, published Oct. 19, 1976, discloses a combination of anion exchange fibers and cation exchange fibers, such as cellulose and vinyl fibers, whose function is to purify sugar syrups.
Japanese Patent Application OPI No. 45,057, published Mar. 13, 1982, relates to ion exchange resins in powder or granular form which are mixed with hydrogel materials, such as self-crosslinked polyacrylate. The ion exchange materials can be anion exchangers or cation exchangers or a mixture of both. The absorbent capacity of the material is said to be less affected by the presence of salts than conventional absorbent materials.